Variable resistor device



0, 1963 w. 'r. HARDISON 3,099,812

' VARIABLE RESISTOR DEVICE Filed Aug. 24, 1961 2 Sheets-Sheet 1 F I INVENTOK WILBUR T. HARDISON United States Patent 3,099,812 VARIABLE RESETQR DEVICE Wilbur 'I. Hardison, 4920 Luther St, Riverside, Calif. Filed Aug. 24, I961, Ser. No. 133,656 14 Claims. (Cl. 338-183) This invention relates to variable resistors comprising a resistance element and a carrier with contact means movable along and in electrical contact with the element, and more specifically the invention relates to improvements in means for actuating the contact-carrier.

In many forms of variable resistors a contact-carrier is moved through a path the extent of which is limited by either the inherent structural characteristics of the resistor housing or structure or by stop means specifically provided for the purpose. The carrier is traversed along the path by actuating means in the form of shaiting, which shafting may comprise a leadscrew or other shaft with which the carrier is suitably engaged to be driven. Thus variation of the value of resistance exhibited between the movable contact and either end of the resistance element is effected by rotation of the shafting. Generally the operating parts of the resistor are enclosed in an opaque housing or casing, with a portion of the shafting protruding from the housing to provide accessibility for actuating the moving parts. As a consequence of the moving parts being hidden from the view, the operator generally does not know the position of the contact relative to the endpoints of its path along the resistance element. As a result the operator may drive the carrier to the limits of its travel quite forcibly, or may attempt to drive the carrier beyond its limits as defined by stops or the like, and so spring or damage the carrier or other part of the operating mechanism. Various clutch means have been heretofore proposed as a remedy for the described difficulty, the clutch means being interposed between two operating parts to allow slippage therebetween when the carrier or contact means reaches either end of its path. The present invention is directed to improvements in contact-carrier driving means of the described character, and particularly to such driving means in extremely small variable resistors wherein space is at a premium and in which weight must be kept at a minimum value.

The present invention utilizes as a slip-permitting link in the carrier-driving or actuating shafting, very small devices that add substantially nothing to the spacerequirements of the variable resistors in which they are used, and which devices are inexpensive and widely used for an entirely different purpose and which consequently add only insignificantly to the cost of the instrument. Essentially the slip-permitting link in the actuating shafting is a small curved strip of spring material such as spring steel. The strip may be coiled into a small cylindrical coil, or may be in the form of a nearly-closed cylinder or longitudinally-split sleeve, as will later be specifically described. The curved strip is radially resilient and hence is susceptible to radial expansion and contraction; and that characteristic is utilized to provide a frictional gripping relationship between a driving means including the curved strip, and a driven means to which the curved strip is applied. The grip may be outwardly,

between an encircling driven means and the encircled curved strip; or the grip may be inwardly directed, as in the case of the driven means comprising the end of a shaft over which the curved strip is applied. The curved strip may in instances and in some applications of the invention be of itself the driving means, or it may be an intermediate member disposed between a driver and a driven means and grippingly engaging both. When expanded and allowed to contract over aligned shaft-ends, or when compressed and allowed to expand outwardly against the wall of a bore formed in a shaft-head, the bent strip provides a means permitting slip to occur between the driver and the driven shaft of the variable resistor, and serves as a friction-clutch which transmits torque without slippage until the contact-carrier is stopped at the end 04: its path, and then slips during further rotation of the driver and thereby prevents springing or other damage to the moving parts of the instruments.

The preceding brief description of the invention makes it evident that a principal object of the invention is to provide improvements in variable resistors actuated by rotation of a shaft.

Another object of the invention is to provide means for obviating damage due to attempted over tr-avel of a contact carrier in a variable resistor.

Another object of the invention is to provide inexpensive means for obviating the effects of attempted overtravel in a shaft-actuated variable resistor.

Another object of the invention is to provide a slippermitting insulative shafiting connection in a shaftactuated variable resistor.

Other objects and advantages of the invention will be made apparent in the appended claims and following description of physical forms embodying the invention which forms are depicted in the accompanying drawings. In the drawings:

FIG. 1 is a pictorial view of a shaft-actuated variable resistor device incorporating the invention;

FIG. 2 is a view of a base member of the variable resistor device depicted in 'FIG. 1;

FIG. 3 is a longitudinal sectional view of the device depicted in FIG. 1, on a larger scale;

FIG. 4 is a transverse sectional view of the device depicted in FIG. 1, taken as indicated by line 44 of FIG. 1, on a larger scale;

FIG. 5 is a sectional view taken as indicated by line 55 in FIG. 3;

FIG. 6 is an exploded view of elements adapted for use in the device of FIGS. 1-5, in disassembled array and with a portion removed;

FIG. 6a is a fragmentary view depicting elements shown in FIG. 6, the elements being in assembled array.

FIG. 7 is a view similar to part of FIG. 6, illustrating a different mode of using a curved strip of spring material to provide a slip-joint;

FIG. 7a is a fragmentary view similar to FIG. 6a, showing details of elements in assembled state;

FIG. 8 is a view similar to FIG. 6, illustrating use of a pin connection of a driver to a screw-threaded actuating shaft and incorporating the principle of the invention;

FIG. 8a is a fragmentary view, with a part broken away to show detail, of elements depicted in FIG. 8, the elements being in assembled array;

FIG. 9 is a view similar to FIG. 8, illustrating the slippermitting elements in a construction not utilizing the pin shown in FIG. 8 and using a simple driven shaft-head;

FIG. 10 is an end-view of a driver depicted in FIGS. 8 and 9;

FIGS. 11 and 12 are views similar to FIGS. 6 and 7, respectively, depicting use of a second species of curvedstrip spring material to provide a slip-joint in variableresistor actuating shafting.

In the drawings, like parts bear like reference ordinals for convenience and correlation in the description of the invention.

There is illustrated in FIGS. 1-5 a variable resistor of one type to which the principles of the invention are applicable and in which the principles have been incorporated to provide an exemplary and illustrative variable resistor according to the invention. In those drawings, 10 indicates that variable resistor device generally. The resistor comprises a base 12 preferably formed as a molding, and a cover 14 which with the base provide a housing for operating parts. As indicated in FIG. 2, the base 12 is formed to provide recesses or slots 16 and 18 separated by an upstanding rib 20. As indicated in FIGS. 3, 4 and 5, the slots 16 and 18 receive an elongate resistance element 22 and a return-conductor 24, respectively. The resistance element, while illustrated as being of the wire-wound variety, may be of any suitable type. The return-conductor 24 is illustrated in the form of a bent plate of metal, of inverted-U cross-section, mounted in slot 18. Suitable insulated electric leads 26, 26a are attached by fusion to respective end portions of the resistance element, lead 26a extending along within the canopy formed by conductor 24, as indicated in FIG. 4. The preceding enumerated parts of the variable resistor may be of any suitable configuration and may, for example, be like or similar to the equivalent parts depicted in U.S. Patent No. 2,777,926, the disclosure of which is incorporated herein by reference.

Disposed above the resistance element 22 and conductor 24 and adapted for wiping movement along and in contact with the element and the conductor is a contact means 28 comprising spaced-apart but electrically interconnected contact points 28a, 2311 which may be parts of an integral conductive contact that is supported on and by a contact-carrier herein shown as a block-like member 3i of insulative material which is proportioned to fit closely the top and sides of cover 14 as indicated in FIG. 4. The contact-carrier or slider may be like or similar to that shown in the aforementioned Patent No. 2,777,926; and is constructed and arranged for traversal along a path extending from one interior end-face of base 12 to the other interior end face, by engagement with a screw-threaded shaft 32 comprised in actuating shafting 'in the variable resistor device. Shaft 32 is journaled at one end in a bore 36 formed in the appropriate end of base 1-2, as indicated in FIG. 3, and at the other end is provided with a driven end journaled in a bore 38 formed in the other end of base 112. The engagement of the contact-carrier means with the screw-threaded shaft whereby the carrier is moved along its path incident to rotation of the shaft, may be by virtue of a tapped bore and interengagement with the thread of the shaft, or by other known means and techniques such as those illustrated in US. Patents 2,886,681; 2,946,975; and 2,898,569.

At the driven end of shaft 32, arrangements are provided for inducing the rotation of the shaft necessary to effect translation of the contact-carrier and the contactmeans along their respective paths in changing the setting of the variable resistor; and for permitting slippage in the actuating shafting if and when the carrier is moved into engagement with either end wall of the housing in which it is disposed. The means for permitting slippage is a curved strip of spring material which yieldingly grips the head of shaft 32 in driving engagement therewith, and which when rotated rotates the shaft until and unless free movement of the slider is impeded. In the latter case, driving effort applied to the curved strip is absorbed in slippage as in a slipping friction clutch. In its simplest form the curved strip of spring material is formed from a substantially rectangular strip by a coiling or wrapping action that results in a nearly closed cylinder; and in a more complex form the strip is rolled into a spiral of more than one turn to form a tubular device. In both forms the resilience of the material permits radial expansion 'or contraction from the relaxed condition, by application of appropriate forces. In both of these forms the curved strip of spring material is commercially available as pins produced for pinning hubs to shafts and the like as substitutes for conventional tapered drive-pins; one form of the commercially available product is marketed under the trade name Roll Pin.

As illustrated in FIGS. 6 and 6a, the head 3211 of screwthreaded shaft 32 is a cylindric extension over which one end portion of the curved strip 40 is adapted to be forced d or positioned by slight expansion of the strip. Therein the driving means for the shaft comprises strip 4t} and a driver 41 having a reduced cylindrical portion 411' similar in configuration to the head 3211 of shaft 352, and a slotted head 4-111 adapted to be rotated by an extraneous tool such as a screwdriver. The driver 41 may have one or more peripheral grooves for reception of D-ring seal means and/or retainer means, as indicated in FIG. 6a and as is understood in the art. In action, as the driver 41 is rotated, the rotational effort is transmitted by strip 40 to head 3211 and the shaft 32 is rotated and carrier traversed along its restricted path in a direction dependent upon the direction of rotation of the driver. Elements if and 40 thus form a driving means that have frictional driving engagement with the driven means comprising head 3211. As is evident, if carrier 30 is traversed so far as to engage an end wall of base 12, rotation of shaft 32 is arrested and slippage occurs between strip 48 and one or both of the cylindrical portions 32/1 and Mr if rotation of driver 41 is continued. As indicated in FIG. 6a, the shaft-driving means comprising driver 41 and strip 48, and head 3211 as well, are rotatably supported in a complementary bore 121' formed in the end wall 12w of base 12 and there retained by a transversely disposed retainer pin P.

In an alternative construction, depicted in FIGS. 7 and 7a, the driven screw-threaded shaft, 32', is provided with a socket head 3271 having a bore 32b into which one end of strip 40 is pressed under radial compression; and the slotted driver, 4-1 is provided with a similar bore 4111 into which the other end of strip 44 is similarly received under radial contraction. Driver 41' may be provided with circumferential grooves as shown, for accommodation of O-ring seal means and a conventional retainer pin P. In other respects the driving means comprising driver and strip 4t) and the driven means comprising head 32/1 function as in the previously described construction except that slippage occurs at the outer surface of strip 4t and the bore formed in end Wall 2 of base 12 is of appropriately difierent dimensions as indicated in FIG. 7a.

In some instances it is desirable that the screw-threaded shaft be insulated from the tool that is applied to the instrument to change the setting. In such instances the modified form of construction illustrated in FIGS. 8 and 8a may be employed. In those drawings the screwthreaded shaft 32 includes at the head end an insulative plug or pin 321 secured in the socket of the head 3212. The pin may be secured in the socket by adhesive 32;; (FIG. 8a), or in any other suitable manner, and may be of alumina or other high-temperature-resistant material. The driver, 41", is a curved strip of spring material like that previously described, and preferably has formed at the outer end thereof suitable tool-engaging notches 4111 (see also FIG. 10) which in effect form a slot for recep tion of a driving tool such as a screwdriver. In this modified form, functioning of the shafting is like that previously described but slippage is limited to slipping between pin 321 and driver 4-1". If desired, high-temperature lubricant such as graphite may be embedded in or adhered to the slip-end of the pin, to obviate wear and/ or to enhance the slipping action to a desired extent. Ooviously, if electrical isolation of driver 41 from the screwthreaded shaft 32' is not essential, pin 321' may be of other than insulative material; or as indicated in FIG. 9, the pin may be omitted and the driver 41 applied directly to the head 3211 of a shaft 32 in the manner depicted in FIG. 6 and heretofore explained in connection with that drawing.

As illustrated in FIGS. 11 and 12, the curved strip of spring material may be in the form of a tubular spirallywrapped roll to provide a strip 48m susceptible of radial expansion and contraction. As there indicated, strip ttlm is adapted to be applied over head 31212 of shaft, and over portion 411' of driver 41]: to form a driving means for driving the shaft, similar in arrangement and action to the structure shown in FIG. 6. Also, as indicated in FIG. 12,

strip 40m may be compressed and expanded within the bore of head 3211 and the bore 41b of driver 41 to similarly form a clutch-like arrangement. The strip 40m is, like strip 40, a commercially available product manufactured as a pin for fastening together parts such as a hub and a shaft through which aligned holes are formed, but wherein, as in the case of the member 40, no slippage occurs. The configuration oi shafting elements shown in FIG. 11 is adapted for use in the base 12 previously described; and the configuration of shafting shown in FIG. 12 is adapted for use in the modified (larger) bore in the base 12 illustrated in part in FIG. 7a. It will be understood that in other respects the two bases 12 and 12' may be substantially the same.

By the preceding description and explanation it has been made evident that the invention provides a simple and inexpensive solution to the problem of broken or stripped parts caused by attempted overtravel of a contactcarrier in a shaft-actuated variable resistor, and that the aforestated objects of the invention have been attained. No additional space is required over that required in similar resistors not incorporating the invention; and in some configurations the total weight may be somewhat reduced. While an exemplary and illustrative preferred physical embodiment of apparatus incorporating the invention has been illustrated and described, it is evident that in the light of the present disclosure changes and modifications may occur to those skilled in the art and accordingly it is not desired to be limited to the exact details of the exemplary apparatus illustrated; but what I claim is:

1. A variable resistor comprising:

first means, including a resistance element, and re turn-conductor means;

second means, including a contact-carrier means and contact-means carried thereby arranged for Wiping contact with said resistance element and said return-conductor means; third means, comprising shafting means, said third means being constructed and arranged for moving said contact-carrier means to traverse said contactmeans along said resistance element and in contact with said return-conductor means, said shaft-ing means comprising driving means and driven means, said driven means including a driven head, said driving means comprising a driver including a curve strip of spring material of generally cylindrical configuration drictionally engaging the driven head, to provide a friction-clutch connection between the driver and the driven means; fourth means, comprising electrical-connection means providing electrical access to end portions of said re sistance element and to said return-conductor means;

and fifth means, comprising housing and support means, for housing and supporting said shafting means and said resistance element and said return-conductor means.

2. A variable resistor according to claim 1, said curved strip of spring material being in the form of a spirallyrolled generally cylindrical body adapted for limited radial expansion and compression.

3. A variable resistor according to claim 1, said curved strip of spring material being in the form of a longitudinally-split tubular sleeve.

4. A variable resistor according to claim 1, said curved strip of spring material being in the form of a longitudinally-split tubular sleeve, said strip being formed to receive an actuating rotary tool.

5. A variable resistor according to claim 1, said driven head having an axial bore and said driver including a head having an axial bore and said heads being disposed with the bores in alignment, and the ends of said curved strip of spring material frictionally engaging the walls of said bores.

6. A variable resistor according to claim. 1, said driven means comprising an insulative shaft-like portion frictionally engaged by said curved strip of spring material.

7. A variable resistor according to claim 1, said curved strip of spring material being in the form of a tubular roll and being formed for rotative engagement of a driver.

8. A variable resistor according to claim 1, said driving means comprising a formed head having a boss and said formed head having means adapted for operative engagement with an applied tool and said driving means further including said curved strip of spring material frictionally mounted on said boss, and said driven head being of cylindric form and irictionally gripped by said curved strip of spring material.

9. A variable resistor comprising:

first means, including an elongate resistance element,

and an elongate return conductor means;

second means, including a contact-carrier means and contact-means carried thereby arranged for wiping contact with said resistance element and said returnrconductor means;

third means, comprising shafting means, said third means being constructed and arranged for moving said contact-carrier means to traverse said contactmeans along said resistance element and said returnconductor means, said shafting means comprising driving means and driven means including a leadscrew disposed for driving engagement with said contact-carrier means, said leadscrew having a threaded portion and a head to be driven by the driving means of the shafting, said driving means comprising a curved strip of spring material adapted for radial compression and expansion and arranged in frictional engagement with the head of said leadscrew for frictionally driving the latter, and said driving means having provision for acceptance of an extraneous implement or tool for actuation by the latter;

fourth means, comprising electrical-connection means providing electrical access to end portions of said resistance element and to said return-conductor means; and

fifth means, comprising housing and support means,

for housing and supporting said first, second and third means.

10. A variable resistor according to claim 9, said leadscrew having a head comprising a section of electricallyinsulative material effective to insulate the threaded portion thereof from the driving means of the shafting.

11. A variable resistor according to claim 9, said driving means comprising a longitudinally-opened sleeve having at one end a frictional gripping engagement with said driven means and at its other end a means adapted [for coaction with a driving tool.

12. A variable resistor according to claim 9, said driving means comprising a spirally rolled strip of spring metal frictionally engaged at one end thereof with said leadscrew and at its other end frictionally engaged with a head comprised in said driving means.

13. A variable resistor according to claim 9, said driven means including on said leadscrew a socket-head and a complementary pin device mounted at one end in the socket of the socket head and gripped at the other end by said curved strip of spring material to be frictionally driven by the latter.

14. A variable resistor according to claim 13, said pin device being of electrically insulative material.

References Cited in the file of this patent UNITED STATES PATENTS 2,069,440 Hathorn Feb. 2, 1937 2,401,351 Herbst June 4, 1946 2,509,058 Haury May 23, 1950 2,777,926 Bourns Jan. 15, 1957 

1. A VARIABLE RESISTOR COMPRISING: FIRST MEANS, INCLUDING A RESISTANCE ELEMENT, AND RETURN-CONDUCTOR MEANS; SECOND MEANS, INCLUDING A CONTACT-CARRIER MEANS AND CONTACT-MEANS CARRIED THEREBY ARRANGED FOR WIPING CONTACT WITH SAID RESISTANCE ELEMENT AND SAID RE TURN-CONDUCTOR MEANS; THIRD MEANS, COMPRISING SHAFTING MEANS, SAID THIRD MEANS BEING CONSTRUCTED AND ARRANGED FOR MOVING SAID CONTACT-CARRIER MEANS TO TRAVERSE SAID CONTACTMEANS ALONG SAID RESISTANCE ELEMENT AND IN CONTACT WITH SAID RETURN-CONDUCTOR MEANS, SAID SHAFTING MEANS COMPRISING DRIVING MEANS AND DRIVEN MEANS, SAID DRIVEN MEANS INCLUDING A DRIVEN HEAD, SAID DRIVING MEANS COMPRISING A DRIVER INCLUDING A CURVE STRIP OF SPRING MATERIAL OF GENERALLY CYLINDRICAL CONFIGURATION FRICTIONALLY ENGAGING THE DRIVEN HEAD, TO PROVIDE A FRICTION-CLUTCH CONNECTION BETWEEN THE DRIVER AND THE DRIVEN MEANS; FOURTH MEANS, COMPRISING ELECTRICAL-CONNECTION MEANS PROVIDING ELECTRICAL ACCESS TO END PORTIONS OF SAID RESISTANCE ELEMENT AND TO SAID RETURN-CONDUCTOR MEANS; AND FIFTH MEANS, COMPRISING HOUSING AND SUPPORT MEANS, FOR HOUSING AND SUPPRTING SAID SHAFTING MEANS AND SAID RESISTANCE ELEMENT AND SAID RETURN-CONDUCTOR MEANS. 